using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{
  protected void Page_Load(object sender, EventArgs e)
  {
    if (!IsPostBack)
    {
      // Fill ListBox dynamically!
      myListBox.Items.Add("Item One");
      myListBox.Items.Add("Item Two");
      myListBox.Items.Add("Item Three");
      myListBox.Items.Add("Item Four");
    }
  }

  protected void btnPostback_Click(object sender, EventArgs e)
  {
    // No-op. This is just here to allow a post back.
  }

  protected void btnAddToVS_Click(object sender, EventArgs e)
  {
    ViewState["CustomViewStateItem"] = "Some user data";
    lblVSValue.Text = (string)ViewState["CustomViewStateItem"];
  }
}